Currently marketed tires are manufactured from materials derived from petroleum resources such that these materials account for half or more of the total weight of the tire. For example, common radial tires for passenger cars contain, based on the total weight of the tire, about 20% of synthetic rubber and about 20% of carbon black as well as aromatic oil and synthetic fibers. Thus, they contain at least 50% of petroleum-derived materials as a whole.
The recent emphasis on the environmental issues, however, has led to tighter CO2 emission restrictions. Moreover, since petroleum raw material is a limited resource and the amount of the material supplied is decreasing year by year, oil prices are expected to escalate in the future and thus the use of petroleum-derived materials has a limit.
Hence, the people's desire to construct a sound material-cycle society has recently become stronger. Accordingly, there is a need for a departure from fossil fuel dependence in the material field as well as in the energy field, and the use of biomass has been focused on.
For example, Patent Literature 1 discloses an environment-friendly tire technology against a future decrease in petroleum supply, according to which a tire is formed in which 75% by weight or more of the total weight of the tire is made from materials derived from resources other than petroleum, for example, by replacing synthetic rubber with natural rubber, carbon black with inorganic filler or bio filler, petroleum oil with vegetable oil or fat, and synthetic fibers with natural fibers.
However, unfortunately, natural rubber is inferior in low-temperature properties and abrasion resistance to synthetic rubber such as polybutadiene rubber.